Coexistence and Competition of Superconductivity and Magnetism in Ho1-xDyxNi2B2C

1
Coexistence and Competition of Superconductivity
and Magnetism in Ho1-xDyxNi2B2C

• Hyeon-Jin Doh, Jae-Hyuk Choi, Heon-Jung Kim, Eun
  Mi Choi, H. B. Kim, B. K. Cho and Sung-Ik Lee
• National Creative Research Initiative Center for
  Superconductivity and Department of Physics,
  Pohang University of Science and Technology,
  Pohang 790-784, Republic of Korea
• M. Ohashi and N. Moˆri
• Institute for Solid State Physics, University of
  Tokyo,
• M. Sigrist
• Theoretische Physik, ETH-Honggerberg, 8093
  Zurich, Switzerland

2

• B. K. Cho, P. C. Canfield, and D. C.
  JohnstonPhys. Rev. Lett. 77, 163-166 (1996), PRL
  77(1996)
• Hyeonjin Doh, Manfred Sigrist, B.K. Cho, Sung-Ik
  Lee Phys. Rev. Lett. 83(25), 5350-5353
  (1999/12/20)
• Jae-Hyuk Choi, Hyeonjin Doh, Eun-Mi Choi, and
  Sung-Ik Lee, M. Ohashi and N. Mori. Phys. Rev. B
  65(2), 024520(6) (2002)
• Jae-Hyuk Choi, Heon-Jung Kim, H. B. Kim,
  Hyeon-Jin Doh, Sung-Ik Lee, and B.K. Cho. Phys.
  Rev. B 72(05), 054516 (2005)

• Contents
• Introduction and Experiments
• Theory and Model
• Results and Discussion
• Summary

3
1. Introduction and Experiments

• History
• Magnetic Superconductor containing the rare-earth
  atoms
• RMo6S8, RMo6Se8, and RRh4B4 (1970s)
• YPd5B3C0.3 with TC 23 K Multi phase
• R. Nagarajan et al., PRL 72
• RNi2B2C (TC 0 16.6 K ) Single phase.
• R. J. Cava et al., Nature 367

4
1. Introduction and Experiments

• Special Feature of Borocarbides
• There exists of compounds to compare
• RNi2B2C R Y, Dy, Ho, Tb, Tm, Er, Lu, Gd
• Underline - magnetism, Red - superconductivity
• TmNi2B2C - TC 11 K, TN 1.5 K
• DyNi2B2C - TC 6 K, TN 10 K
• HoNi2B2C - TC 8 K, TN 5 K
• High quality samples can be produced in single
  crystal form.

5
Superconducting Transition Temperature and
de-Gennes Factor
6
Motivation
7
Motivation
8
1. Introduction and Experiments

• Electrical properties
• Layered structure. But!! It shows 3D nature.
• Large N(eF) 2.4 states/eV Ni relatively high
  TC.
• Multiband system.
• All bands contribute to the superconductivity.
• Most contribution comes from Ni(3d).
• Magnetic properties
• Originated from the 4f orbitals of the rare-earth
  atoms. RKKY interaction between the local
  moments.
• Large Spin-Orbit coupling.
• -Strong anisotropy Crystal Electric Field
  Effects.

9
1. Introduction and Experiments

• Crystal Structure

• Magnetic Structure

10
1. Introduction and Experiments

• TC suppresion by Dy dopping into HoNi2B2C.
• TN scales with de Gennes factor.
• TC does not fit with de Gennes scaling
• B. K. Cho et al. PRL 77(1996)

11

• Strange HC2 curve

Canfield et al., Physics Today 51

12
1. Introduction and Experiments

• Neutron scattering
• Spiral phase

Q(0,0,2p)
Q(0,0,2p)
Q(0,0,2p)
J. W. Lynn et al. PRB 55(1997)
13
2. Theory and Models

• Model for the magnetic order
• The free energy from spin degree of freedom.
• Here, and
• - Coupling between antiferromagnetic
  order and the spiral order.
• Two orders compete each other ( ).

14
2. Theory and Models

• Magnetic fluctuation
• Antiferromagnetic order.
• Antiferromagnetic fluctuation.
• Mean Field Calculation by using.
• The increase of the free energy due to the
  magnetic fluctuation.

15
2. Theory and Models

• Calculation of
• Gaussian Fluctuation.
• Experiment for comparing.

16
2. Theory and Models

• Superconducting order
• Multiple bands system.
• Ni(3d), B(2p)-C(2p), and R(5d)
• All bands contribute the superconductivity.
• In ordered states, the magnetic moments are
  cancelled in Ni plain.
• Two order parameter.
• From Ni band.
• From the bands other than Ni.

Observation of a Pair-Breaking Field at the Ni
Site in Nonsuperconducting ReNi2B2C, PRL 76,
507-510 (1996) E. Baggio-Saitovitch, Brazil
17
Theory and ModelsMossbauer Results
Temperature dependence of local magnetic field at
the 57Fe nucleus in TbNi2B2C and HoNi2B2C
18
2. Theory and Models

• Free energy for two superconducting orders.
• ?A- superconducting order from Ni(3d)bands.
• ?B- superconducting order from the other bands.
• ?1,2 - Josepsen coupling between ?A and ?A

19
3. Results and Discussion

• TC suppresion
• The linearized Ginzburg-Landau equation.

20
3. Results and Discussion

• HC2 curve
• Comparison with the experiments

Canfield et al., Physics Today 51
HoNi2B2C DyNi2B2C
21
3. Results and Discussion

• Pressure Effects
• Transport experiments of Ho0.9Dy0.1Ni2B2C and
  Ho0.6Dy0.4Ni2B2C.
• For TNltTC,
• dTC/dp -0.64 K/Pa.-0.49 K/Pa Michor, PRB 61
• dTN/dp 0.48 K/Pa.0.482 K/Pa Michor
• For TNgtTC,
• TC almost constants.

Solid square TC in exp Solid circle TN in
exp Solid line TN in theory Dotted line TC in
theory J.-H. Choi, PRB 65
22
3. Results and Discussion

• Reentrant behavior of Ho1-xDyxNi2B2C

B. K. Cho et al., PRL 77 (1996)
Schematic diagram for the resistivity data
23
3. Results and Discussion

• Qualitative description for Lu1-xDyxNi2B2C

• From the DyNi2B2C side, if we put in Lu instead
  of Dy, this breaks the balance which makes zero
  field at Ni site.
• Lu acts as magnetic impurity, through Lu has no
  magnetic moments.
• Increasing Dy reduces the magnetic fluctuation.
  This enhances the superconductivity.

B. K. Cho et al., PRL 77 (1996)
24
3. Results and Discussion

• Qualitative description for Dy1-xTbxNi2B2C

J. H. Choi et al. (1999)
Magnetic structure
25
3. Results and Discussion

• TC suppression of Dy1-xTbxNi2B2C
• Tb has different type of magnetic order from Dy
  and Ho.
• The magnetic field at Ni site is not zero in
  TbNi2B2C at T lt TN
• Tb suppresses the superconductivity from Ni bands
  unlike Ho and Dy.
• Breakdown of the de Gennes scaling of TN.
• Since Tb and Dy has different type of magnetic
  order, they suppress each other and TN is lower
  than expected from the de Gennes scaling.

26
4. Summary

• RNi2B2C is multi-band system unlike the cuprate.
• There are many contributions for the
  superconductivity.
• In HoNi2B2C and DyNi2B2C, two superconducting
  order parameters are introduced due to the
  magnetism.
• One interacts with the antiferromagnetic order
  and the other does not.
• Phenomenological theory describes well.
• TC and TN in Ho
• HC2 of HoNi2B2C and DyNi2B2C.
• Pressure dependence.
• Reentrance behavior of HoNi2B2C.

27
4. Summary

• In Lu1-xDyxNi2B2C, Lu breaks the balance of the
  magnetic field and generate the field at Ni site.
• Lu acts as a magnetic impurity in the Dy
  background.
• In Dy1-xTbxNi2B2C, the structure of the
  antiferromagnetic order is different from
  Ho1-xDyxNi2B2C.
• The antiferromagnetic order suppresses the
  superconductivity from Ni bands.